Apparatus and method for determination of one or more free neutron characteristics

ABSTRACT

A neutron detection system may include a neutron detector including a plurality of neutron detection devices, a plurality of discrete neutron moderating elements, wherein each of the neutron moderating elements is disposed between two or more neutron detection devices, the plurality of neutron detection devices and the plurality of discrete neutron moderating elements disposed along a common axis, a control system configured to generate a detector response library, wherein the detector response library includes one or more sets of data indicative of a response of the detector to a known neutron source, receive one or more measured neutron response signals from each of the neutron devices, the one or more measured response signals response to a detected neutron event, and determine one or more characteristics of neutrons emanating from a measured neutron source by comparing the one or more measured neutron response signals to the detector response library.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is related to and claims the benefit of theearliest available effective filing date(s) from the following listedapplication(s) (the “Related Applications”) (e.g., claims earliestavailable priority dates for other than provisional patent applicationsor claims benefits under 35 USC §119(e) for provisional patentapplications, for any and all parent, grandparent, great-grandparent,etc. applications of the Related Application(s)).

RELATED APPLICATIONS

For purposes of the USPTO extra-statutory requirements, the presentapplication constitutes a regular (non-provisional) patent applicationof United States Provisional Patent Application entitled APPARATUSES ANDMETHOD FOR THE IDENTIFICATION OF FREE NEUTRON PROPERTIES, naming StevenL. Bellinger et al. as inventors, filed Oct. 27, 2011, Application Ser.No. 61/198,413.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of Award ONRN00014-11-1-0157, ONR N00014-11-M-0041, and DTRA-01-03-C-0051.

TECHNICAL FIELD

The present invention generally relates to a method and apparatus forneutron detection, and more particularly to a neutron detection systemallowing for more efficient detection of neutrons.

BACKGROUND

Neutron detection is a challenging task due to the fact that neutronshave no distinguishing charge, in contrast to alpha particles, betaparticles, or excited electrons from gamma ray interactions. Typically,neutrons are detected through nuclear reactions, such as absorption orscattering reactions. However, those nuclear reactions tend to causeenergy identification of the neutrons to be lost, thereby making neutronspectroscopy difficult to realize. Several methods have been proposed tomeasure neutron spectra from unknown (or known, but uncalibrated)sources. Some of the methods are briefly reviewed below.

The “Bonner Sphere” detection method consists of a small neutronsensitive scintillation detector inserted in a high-density polyethylene(HDPE) ball. The system consists of a set of balls, ranging from 3inches in diameter up to 14 inches in diameter. A measurement is madewith each ball, one after the other, under identical operatingconditions. From known response curves, the neutron spectrum can beback-calculated from the data through unfolding techniques. Most changesare greatest for neutrons under 1 MeV. However, for neutrons greaterthan 1 MeV, the neutron detection response curves for the Bonner sphereset are very similar. In addition, the mass of the spheres and themethod used makes Bonner spheres impractical for fast and/or portableneutron spectroscopy.

A nuclear plate camera can be used to discern neutron energies. Thesystem consists of a HDPE radiator fastened to the front of a vacuumcylinder or box. Fast neutrons interacting in the plastic eject recoilprotons, with the most energetic protons being completely forwardscattered. A film plate, set at 10 degrees from normal, is located atthe end of the box. A series of collimators ensures that only forwardscattered protons reach the film plate. Proton interactions in the filmproduce a measurable track, the length of which correlates to theforward scattered energy of the proton, and therefore the neutronenergy. The film must be developed; therefore, immediate interpretationof the results is difficult or impractical.

The ³He device depends upon the ³He(n,p)³H reaction, with a Q=0.764 MeV.Fast neutrons absorbed in the ³He gas produce energetic charged particlereaction products with total energy equal to the initial neutron energyplus 0.764 MeV, thereby allowing for the original neutron energy to becalculated. Additionally, fast neutron recoils off of the ₃He gasproduce a noticeable recoil peak at 75% of the initial neutron energy,giving a second method to check the initial neutron energy. Gas recoildetectors rely solely upon fast neutron scattering reactions; hence thedevices typically use hydrogen, or a hydrogen gas mixture, or helium.The recoil peak established on a pulse height spectrum allows for thecalculation of the initial neutron energy.

The proton recoil telescope system is similar to the nuclear-platecamera, except charged particle detectors are set at known angles withrespect to the HDPE radiator. Hence, the energy deposited in the chargedparticle detector, along with the angle of incidence, yields the initialneutron energy. However, the concept relies on the fact that the initialtrajectory of the fast neutron is known; hence the origin of the fastneutrons must be given.

Time of flight spectrometers rely upon the velocity and energycorrelation with neutrons. A set of “choppers”, slotted cylinders withvariable angular velocities, are set apart by a significant distance.The rotating slots are synchronized such that neutrons of apre-established velocity can pass through both choppers, but the secondchopper will block slower or faster neutrons. A detector is locatedbeyond the second chopper, which will detect only those neutrons thatcan pass through the entire apparatus. By adjusting the chopper angularvelocities for each measurement, a spectrum of the neutron field can bemeasured provided that the direction from which the neutrons are comingis known. Typically, time of flight spectrometers tend to be relativelylarge and lacking portability.

Plastic scintillators rely upon (n,p) reactions to produce measurablescintillation light. The recoil protons produce scintillation light as afunction of energy. The scattered neutron may lose all of its energy ina single collision, thereby giving all of its energy to the recoilproton. Alternatively, the neutron may lose its energy through a seriesof scatters, thereby distributing its energy to many protons. The lightis measured with a photomultiplier tube, or some other light-sensingdevice. Some problems with plastic scintillators are: (a) their lightemission spectrum is non-linear with respect to energy deposition andparticle mass; (b) they are fairly insensitive for proton recoils withenergy less than 1 MeV; and (c) the scintillator mass (volume) requiredto stop energetic neutrons is significant, hence Compton electronsexcited by gamma ray interactions in the material can contribute tobackground noise.

The capture-gated neutron spectrometer utilizes a plastic scintillatorthat has been doped with ¹⁰B. Recoil reactions (n,p) occur rapidly andproduce scintillation light from recoil protons with about 50 ns, whichcan yield the total energy of the original neutron provided that all ofthe neutron energy is absorbed in the scintillation block. Thermalizedneutrons can diffuse to a boron site, which can take severalmicroseconds, after which another scintillation flash will be observedfrom the ¹⁰B(n,α)⁷Li reaction (Q=2.31 MeV). If the second flash occurs,equivalent to 2.31 MeV energy deposition, then the first flash isindicative of the original neutron energy. If a second flash does notoccur, then the first flash is ignored as having been produced bypartial energy deposition of the neutron. The system suffers from thenon-linear light emission attributes of plastic scintillators.Furthermore, completing processes with carbon scattering in thescintillator tends to enhance the non-linear response.

Five classes of wide energy range and non-time-of-flight neutronspectrometers have emerged over time, including: (1) single detectorsenclosed by multiple neutron interaction materials; (2) multipledetectors individually enclosed by different neutron interactionmaterials; (3) multiple detectors collectively enclosed by a singleneutron interaction material; (4) single position sensitive detectorsenclosed by multiple neutron interaction materials; and (5) instrumentswhich comprise a combination of elements from the first three.

In the first class, a combination of boron and/or cadmium, lead ortungsten, and high hydrogen concentration material (usually, highdensity polyethylene [HDPE]) are used as filters, spallation centers,and moderators to provide ever better response up to ones of GeVincident neutron energy (e.g., Can berra's SNOOPY or Thermo'sSWENDI-II). These instruments are known colloquially as theAndersson-Braun (AB) type. The downside of this approach is that thetotal mass is high (usually >10 kg) and the intrinsic detectionefficiency is low.

In the second case, multi-band detectors usually tune three or moredetectors to the thermal, epithermal, and fast neutron spectrum rangesbut without extraneous moderator. The implication here is a lightweightinstrument (e.g., Ludlum's PRESCILA). However, the average energyresolution over the thermal to fast range is consequently the poorest ofthe five methods because of severe over or under response in the bandsnot covered.

The third method employs many individual thermal neutron detectors in anHDPE or comparable moderating matrix to provide a depth dependentintensity of thermalized neutrons that yields both the highestefficiency and lowest average dose- and dose-rate-error of the abovemethods. The shortfall of these instruments is their large moderatingvolume (usually a 30 cm diameter sphere) needed to accommodatetens-to-hundreds of individual detectors, rendering a non-portabledevice (>40 lbs with electronics).

The fourth method utilizes a single position sensitive detector enclosedby moderator and filter materials as an improvement to the classicallong counter. This detection scheme suffers from large moderatingvolumes and low intrinsic efficiency due to high neutron absorption inthe moderator and/or scattering of neutrons outside the detector volume.

There are only a few examples of the fifth class which utilize acombination of elements from the first three. Like the second class,these dosimeter schemes use a superposition of responses, but theyincorporate an important improvement in that the overlapping energyresponse bands are continuous providing for a much better doseequivalent match. The downside is again the large total volume and lowintrinsic efficiency.

Passive identification and/or differentiation of spontaneous fission(e.g., ²⁵²Cf), radioisotope (α,n) (e.g., AmBe), and/or spallation (e.g.,cosmic-ray induced) neutrons sources represents a significant challenge.High total or intrinsic neutron detection efficiency over the specifiedenergy range is important with regard to collection time and in beingsensitive to the bare, filtered, and/or moderated incarnations of theabove identified neutron sources. Spectroscopic resolution is importantas it provides a means of deconvolving, identifying, and/or verifyingknown and unknown neutron sources. Portability is important with regardto man-based searches. For example, the SNOOPY NP-2 neutron REM metercurrently used onboard nuclear Navy ships weighs 22 lbs. and preventssailors from performing their job as well as they could if a lighter REMmeter were made available. Direct or effective insensitivity to photons,which could swamp out or be recorded as false positive neutrons, isespecially prudent given the ease through which gamma emitters naturallyexist, are omni-present with any neutron source, and can intentionallybe placed as a red herring by those wishing to thwart neutron presenceand properties. Determination of absolute neutron flux is useful towardverification of source strength and in displaying the real-time ambientneutron dose equivalent. Ambient neutron dose equivalent is an importantmeasure of absorbed dose, weighted for the energy(ies) of the absorbedneutron(s). Some real-time portable REM meters yield incredible error,especially in the epithermal neutron energy range. Given not only thedearth of ³He, but the flux and spectral variance of neutrons andphotons, there exists a need for neutron sensitive instruments that cureat least some of the foregoing deficiencies and enable performanceattributes desired in the art.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not necessarily restrictive of the invention as claimed. Theaccompanying drawings, which are incorporated in and constitute a partof the specification, illustrate embodiments of the invention andtogether with the general description, serve to explain the principlesof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The numerous advantages of the disclosure may be better understood bythose skilled in the art by reference to the accompanying figures inwhich:

FIG. 1A through 14F illustrate various embodiments of the system fordetermining one or more free neutron characteristics, in accordance withthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not necessarily restrictive of the invention as claimed. Theaccompanying drawings, which are incorporated in and constitute a partof the specification, illustrate embodiments of the invention andtogether with the general description, serve to explain the principlesof the invention. Reference will now be made in detail to the subjectmatter disclosed, which is illustrated in the accompanying drawings.

Referring generally to FIGS. 1A through 14F, a neutron detection system100 suitable for determination of one or more free neutroncharacteristics is described in accordance with the present disclosure.The present invention is directed to a low-power high-efficiencysemiconductor thermal-neutron detector disposed within a neutronmoderating volume. The present invention is further directed to aportable neutron detector unit (e.g., hand-held unit, shoulder carriedunit, or the like) and may be powered utilizing battery power. In afurther aspect, the neutron detection system 100 of the presentinvention is suitable for performing neutron energy spectroscopy ormeasuring quantities correlatable to neutron energy, allowing for thedetermination of various neutron energy characteristics, such as, butnot limited to, neutron source type and neutron dose. The spectroscopicabilities of the detector 102 of the present invention allow for thediscernment of various neutron sources, such as spontaneous neutronemitters (e.g., Cf), (α,n) emitters (e.g., Am—Be, Pu—Be, and the like),spallation neutron emitters, fusion-based neutron emissions (DD, DT, TT,etc.) and photoneutron (γ,n) sources (e.g., Sb—Be). In addition, thedetection system 100 is suitable for detecting incident neutrons as afunction of directional incidence, allowing the detection system 100 toeffectively act as a directional sensor. In this regard, the detectionsystem of the present invention is commonly referred to herein as aneutron detector as well as a neutron spectrometer.

FIGS. 1A-1B illustrate a high-level block diagram of the neutrondetection system 100, in accordance with one embodiment of the presentinvention. In one aspect of the present invention, the neutron detectionsystem 100 includes one or more neutron detectors 102. In a furtheraspect, the one or more detectors 102 may include, but are not limitedto, a plurality of neutron detection devices 104. In another aspect ofthe present invention, the neutron detection system 100 includes acontrol system 108 communicatively coupled to an output of each of theneutron detection devices 104, or coupled to an output of the detectionelements 105 of each device 104, of the one or more detectors 102.Additionally, the control system 108 may include one or more processingelements 110 (e.g., computer processor, FPGAs, ASICs, and the like).Further, the control system 108 may include, but is not limited to, anon-transitory storage medium 112 (i.e., memory medium) containingprogram instructions configured to cause the one or more processingelements 110 to carry out one or more of the various steps (e.g., systemcontrol steps, data analysis steps, and the like) described through thepresent disclosure.

In another aspect of the present invention, the one or more processingelements 110 of the control system 108 are configured to: receive one ormore output signals from the one or more neutron detection devices 104of the one or more detectors 102 and determine (e.g., determine inreal-time, near real-time, or delayed time) one or more characteristics(e.g., energy, energy spectrum, neutron source type, direction ofneutron emanation, dose, flux, and the like) of neutrons 103 (e.g.,neutron emanating from neutron source 101) impinging on the one or moredetection devices 104. In a further aspect of the present invention, thecontrol system 108 may be communicatively coupled to a user interfacedevice 116 (e.g., display device 117 and user input 119).

FIGS. 1C-1E illustrate a schematic view of a neutron detector 102 of thedetection system 100, in accordance with one embodiment of the presentinvention. In one embodiment, the detection devices 104 of the neutrondetection system 100 may be disposed within a volume of neutronmoderating material 109 (e.g., continuous volume of moderating materialor volume of moderating material formed with discrete moderatingelements 106). In an additional embodiment, as shown in FIG. 1E, one ormore of the neutron detection devices 104 may include two or moreneutron detection elements 105 (e.g., independent neutron reactiveelements) suitable for detecting impinging neutrons.

In another embodiment, the neutron detector 102 may include one or moreneutron absorber elements 120 positioned between at least some of thedetector devices 104 and moderator elements 106, as shown in FIG. 1C.For the purposes of the present disclosure, the absorber elements 120may also be referred to as “backscatter stoppers” 120. In a furtherembodiment, each moderating element 106 is bounded by one of theabsorber elements 120, whereby the absorber elements 120 are configuredto confine scattered neutrons to the given moderator element in whichthe neutrons initially reach thermal energies. In one embodiment, theabsorber elements 120 may consist of a volume of material disposedwithin a moderating neutron spectrometer volume in the proximity of oneor more detecting devices 104 and are configured to capturebackscattered neutrons (with the greatest probability at the energywhere the cross section for capture by the absorber element is highest).Applicants note that by capturing backscattered neutrons the scatteringdependent intensity along one or more coordinate directions becomes morepronounced due to less blurring, resulting in a more unique scatteringintensity. The reduced smearing represents an improvement on classicalmoderating type neutron spectrometer systems in which scatteringdependent intensity along one or more coordinate dimensions issignificantly blurred (significant overlap in the response functions ofthe detection elements) which leads to reduced energy resolution orenergy metric resolution.

In a further embodiment, the detector 102 of the detection system 100may be surrounded by an electromagnetic lightproof shield 122. Inanother embodiment, a neutron and/or background radiation shield 126 maybe disposed about the exterior portion of the detector 102. In anadditional embodiment, a set of data acquisition (DAQ) and/or controlcircuitry elements 124 may be disposed in proximity to the one or moredetection devices 104 and within the internal volume of the detector102.

Applicants note that the spatial resolution of the locations of neutroninteraction events (e.g., capture, induced-fission or scattering events)within the neutron detector 102 allows for the determination, by controlsystem 108, of one or more energy or spatial characteristics of theneutrons 103 emanating from the neutron source 101. The one or moreenergy or spatial characteristics include, but are not limited to,energy, energy spectrum, dose, source type and/or the spatial point ofemanation of the impinging neutrons (e.g., isotropic incident neutrons,anisotropically incident neutrons, or parallel incident neutrons).

Further, the present invention also provides for high intrinsicefficiency (i.e., intrinsic efficiency to ²⁵²Cf) detection of neutronsimpinging on the neutron detection system 100 over the thermal to fastneutron energy range. Most neutron reactive materials, such as, but notlimited to, boronated materials or lithiated materials, suitable for usein the neutron detecting system 100 of the present invention have agreater probability of capturing thermal neutrons than higher energyneutrons. One way to efficiently capture incident higher energy neutrons(e.g., fast neutrons) is to embed the given one or more detectiondevices 104 at a selected depth (or depths) within a neutron moderatingmaterial 109. As a result, neutron detection devices 104 disposed nearthe surface of the neutron detection system 100 are more sensitive toneutrons impinging on the surface of the detector 102 at thermalenergies than neutron detection devices 102 disposed at larger depths,which are more sensitive to initially fast neutrons, which arethermalized by the intervening neutron moderating material 109 (e.g.,high density polyethylene). By arranging the neutron detection devices104 at progressively larger distances (e.g., linear spacing ornon-linear spacing) from a surface of the moderating material 109 andcreating multiple independent neutron detection elements 105 (althoughthis is not a requirement of the present invention) in the various solidstate neutron detection devices 102 it is possible to determine variousenergy or spatial characteristics of the impinging neutrons 103 (e.g.,energy spectrum, dose, source type, direction of emanation of impingingneutrons and the like). Real-time determination of incident neutronenergy and direction of emanation allows for the statistical inferenceof conditions related to the given neutron source 101. For example, bymeasuring the incident neutron energy spectrum and the directionality ofincident neutrons it is possible to deduce the type of neutron source(e.g., cosmic-ray production of neutrons, weapons grade plutoniumsource, or plutonium-beryllium source for scientific research).

In one embodiment, the one or more detection devices 104 may include,but are not limited to, microstructured semiconductor neutron detectors(MSNDs). In one embodiment, the MSND-based semiconductor devices of thepresent invention may include devices consisting of a semiconductorsubstrate including microscopic cavities (e.g., holes) etched into thesemiconductor surface, whereby the etched cavities are subsequentlyfilled with a neutron reactive material, such as ¹⁰B or ⁶LiF submicronpowders. It has been shown that these devices may be capable of thermaldetection efficiencies exceeding 35%.

In a further embodiment, the MSND-based detection devices 104 of thesystem 100 may be formed by etching cavities into float-zone-refined(FZR) Si to produce a selected pattern (e.g., overall hexagonal orsquare pattern). The cavities may be etched so that they do not reachcompletely through the device. In this embodiment, holes or trenches ofvarious shapes are etched into the semiconductor surface, wherein thetrenches may extend across the semiconductor substrate and are etchedalmost through the substrate and are subsequently filled with neutronreactive material. Microstructured Neutron Detection devices aredescribed in detail by McGregor et al. in U.S. Pat. No. 7,164,138,issued on Jan. 16, 2007, and U.S. Pat. No. 6,545,281, issued on Apr. 8,2003, which are incorporated herein by reference in their entirety.

In another embodiment, the one or more detection devices 104 mayinclude, but are not limited to, semiconductor devices coated in aneutron reactive material. For example, the one or more detectiondevices 104 may include, but is not limited to, a semiconductor devicecoated in ¹⁰B or ⁶LiF.

In another embodiment, as shown in FIGS. 1C-1H, the individual neutrondetection devices 104 that make up the plurality of the detectiondevices 104 may have a substantially planar shape. For example, one ormore of the neutron detection devices 104 may include a detection device104 having a geometrical shape with very high aspect ratio (i.e., verythin). For instance, the neutron detection devices 104 may include aflat circular shaped neutron detection device, such as the disc-shapeddetector device 104 shown in FIG. 1H. Applicants note that a variety ofgeometrically shaped neutron detection devices 104 are suitable for usein the neutron detection system 100, including, but not limited to,rectangles, squares, circles, ellipses, triangles, or hexagons.Applicants note that any geometrical shape may be implemented providedit yields a translatable pattern that can be tracked along one or morecoordinate axes. It is further contemplated that, while planar-shapeddetection devices 104 may serve as the most easily fabricated devices,devices may also be fabricated individually and embedded at thelocations necessary to obtain a coordinate dependence of the neutroncapture, induced-fission or scattering intensity. It should berecognized by those skilled in the art that the use of planar detectiondevices 104 is not a limitation and that the implemented neutrondetection devices 104 may have a substantially non-planar character(e.g., devices having low aspect ratio) as long as they represent avolume along a determined coordinate axis. For instance, one or more ofthe neutron detection devices 104 may have a ribbon shape, or packing ofcubes.

In a further embodiment, the plurality of neutron detection devices 104may be disposed within a neutron moderator material 109 such that one ormore of the neutron detection devices 104 are aligned in a substantiallyparallel manner. For example, as shown in FIGS. 1C-1D, nine individualneutron detection devices 104 are aligned such that the surfaces of theindividual devices are substantially parallel with respect to oneanother. For example, a first detection device, a second detectiondevice, and up to and including an Nth detection device may be alignedsuch that the surfaces of the individual devices 104 are substantiallyparallel with respect to one another.

In another embodiment, the plurality of neutron detection devices 104 ofthe neutron detection system 100 may include a ‘stack’ of a selectednumber of individual detection devices 104. For example, a stack of aselected number of substantially planar and parallel aligned neutrondetecting devices 104 may be disposed within a volume of a chosenneutron moderating material 104. For instance, as shown in FIGS. 1E and1F, a stack of eight substantially planar and parallel aligned neutrondetection devices 104 are embedded within a volume of a selectedmoderating material 109. In another instance, as shown in FIGS. 1C-1D, astack of nine substantially planar and parallel aligned neutrondetection devices 104 are disposed within a moderating material byarranging each of the internal devices between two moderator slabs 106(e.g., cylinders). It should be recognized by those skilled in the artthat the use of eight or nine devices is not a limitation and that theneutron detection system 100 may employ any number of detection devices104, based on the specific demands on the detection system 100. It isnoted herein that increasing the number of detection device layers inthe neutron detection system 100 may improve both neutron captureefficiency and neutron spectral and directional measurement accuracy upto the limit at which the moderator in between planar devicescompromises the scattering-energy (i.e., moderation) relationship.

In one embodiment, the moderating volume 109 may substantiallyencapsulate the detection devices 104, as shown in FIG. 1E. In anotherembodiment, the moderating volume 109 may include a set of discretemoderating elements 106, such as, but not limited to, a set of cylindersor blocks of moderating material positioned between adjacent detectiondevices, as shown in FIG. 1C-1D. In a further embodiment, in acylindrical shaped detector 102 as shown in FIGS. 1C-1D, a series ofcylinder shaped moderating elements 106 may be positioned betweenadjacent detector devices 104. Suitable neutron moderating materialsinclude materials with a high content of low atomic weight atoms havinga relatively large cross section for neutron scattering but a relativelylow neutron capture cross sections, such as hydrogen, boron-11,beryllium, carbon and nitrogen. For example, suitable moderatormaterials include, but are not limited to, elemental, compounded, ormixture form of water (e.g., light or heavy), organic compounds, such ascarbon-based polymers (e.g., plastics, polyethylene, high densitypolyethylene, and the like), granular inorganic materials, and graphite.For instance, each of the moderator elements 106 of the detector 102 maybe formed from high density polyethylene (HDPE). It should be recognizedthat the use of a HDPE as a neutron moderator is not a limitation andthat the neutron detection devices 104 may be embedded or surrounded byother suitable neutron moderating materials. It will be recognized bythose skilled in the art that the choice of neutron moderator materialwill depend on the exact purposes of the given neutron detection system100 and different moderators may be more or less suitable in differentcontexts (e.g., size limitations, portability requirements, energysensitivity requirements, or directional sensitivity requirements). Theuse of HDPE and other moderator materials for moderating neutrons in aneutron detection setting is described in U.S. Pat. No. 7,514,694 filedon Jun. 19, 2007 which is incorporated herein by reference.

In another embodiment, materials suitable for the neutron absorberelements 120 may include, but are not limited to, elemental, compounded,or mixture form of cadmium, gadolinium, boron, lithium, indium, iron,lead, and mercury. Applicants note that the absorber element 120 may beconfigured to reduce the likelihood that a backscattered and thermalizedneutron is not detected short of where it should have been detectedwould the neutron have only lost energy (elastically scattered) throughforward scattering alone. In this sense, neutron capture materials withlarge cross sections in epi-thermal and higher energy regions (e.g., Br)may also be useful in improving the “uniqueness” of the neutronintensity along one or more coordinate directions (much like a filtereffect).

In one embodiment, as shown in FIGS. 1C-1D, the neutron detector 102 ofthe detection system 100 may include a snout assembly 113 configured toensure the neutrons detected within the internal volume of the detectorare epithermal or faster neutrons.

In one embodiment, the snout assembly 113 includes a first thermalneutron detection device 104 (in this case the left-most detectiondevice 104), a backscatter blocker/absorber 107 and a void region 111.The first neutron detection device 104 may consist of any neutrondetection device described in the present disclosure. In one embodiment,the first neutron detection device 104 may include a high efficiencysemiconductor detection device. The first detection device 104 isfastened to the front of the detector 102, so as to be the initialdetector that neutrons potentially interact with. In a furtherembodiment, directly behind the neutron detection device 104 is aneutron absorbing sheet 107 (e.g., Cd sheet) configured to preventbackscattered thermal neutrons from entering the front neutron detectiondevice 104 from behind (i.e., from the right side in FIG. 1C-1D). Sincethe device incorporates numerous cylinders (e.g., high-densitypolyethylene (HDPE) cylinders) as moderators, it becomes important foranalysis purposes that the neutrons that interact in the front thermalneutron detection device are from thermal neutrons initially enteringthe detector 102. The blocking/absorbing disk 107 behind the frontdetection device 104 also ensures that no thermal neutrons reach thespectral detection devices 104 from outside and that all thermalneutrons detected in the main body of the detector 102 are a result ofincident epithermal and fast neutrons that have been thermalized in themoderator elements 106 of the detector 102.

In a further embodiment, behind the front end detection device 102 andabsorbing disk 107 is a void region 111 configured to reduce the numberof captured gamma rays produced in the moderator (e.g., Cd) disk fromentering the spectrometer 102 body by reducing the solid angle to thesecond detection device 104 (located behind the first moderator disk106). Following the void region 111 is a series of high-efficiencyneutron detection devices 104, absorber shields 120, and moderatorelements 106, as described throughout the present disclosure. The HDPEmoderators reduce the energy of the neutrons, thereby increasing theprobability they will be absorbed within an adjacent semiconductordetection device 104. Fast neutrons can penetrate much deeper thanepithermal neutrons, hence the detector interaction distribution yieldsthe probable neutron energy distribution from the source 101. To preventmigration of thermalized neutrons from backscattering into frontwarddetection devices, absorber shields (e.g., Cd shields) are placed behindevery semiconductor neutron detection device. In the case ofCadmium-based absorber shields, such a precaution helps ensure thatsub-cadmium neutrons interact only in the detection device 104 adjacentto the moderator cylinder in which the neutron is moderated below the Cdcutoff energy. Although FIGS. 1C-1D show only sixdetector/absorber/moderator stacks, the actual design may incorporate upto 20 or more such stacks. As such, the fine distribution of detectiondevices 104 dispersed within the detector allows for discernment of theincident neutron energy spectrum. Further, the design allows fordiscernment of epithermal neutrons.

The canister inside which the detectors are stacked is designed with thefollowing design criteria. First, signals from the semiconductor neutrondetectors must be extracted from the unit efficiently. Second, afterneutrons have scattered out of the column of moderators, retry into thecolumn of thermalized neutrons must be effectively eliminated. Third,thermalized neutrons must not be allowed to enter the main body of thedevice from the sides, only neutrons incident from the front can enterthe moderator-detector stack.

In another embodiment, a canister lining configured to align themoderators 106 in a row is fabricated from a lightweight electromagneticinterference shielding metal (e.g., aluminum) in order to shield theneutron detection devices from interference. In another embodiment, onthe inside of the lining is a sleeve of Cd, which eliminatesbackscattered sub-cadmium neutrons from reentering the HDPE column afterscattering out. Surrounding the Al tube containing thedetector-moderator stack is a cylindrical annular sleeve of borated HDPEto prevent neutrons incident on the side of the device from reaching thedetector-moderator stack. The back of the device may have a similarexternal neutron shield.

In another embodiment, the neutron detection devices 104 of theplurality of neutron detection devices 104 may be positioned along acommon orientation axis. For example, as illustrated in FIG. 1C-1F, theneutron detection devices 104 may be spaced linearly along an axialdirection. For instance, the neutron detection devices 104 within astack of neutron detection devices may be periodically spaced along acommon axis at selected interval (e.g., 0.25 to 2 cm interval). Itshould be recognized by those skilled in the art that the specificlinear spacing interval of neutron detection devices 104 is not alimitation and that various spacing intervals may be used in the neutrondetection system 100, with the specific spacing chosen according tospecific efficiency, accuracy, and sensitivity requirements of the givensystem. By way of another example, the neutron detection devices 104 ofthe detector 102 may be spaced nonlinearly along a common axis. Forinstance, the neutron detection devices 104 within a stack of neutrondetection devices 104 may be spaced along a common axis at intervals of0.5, 1.0, 1.5, 2.0, 3.0, 5.0, 7.5, 10, 15, and 20 cm, as measured from asurface of the detector 102. It should be recognized by those skilled inthe art that the specific nonlinear spacing intervals of neutrondetection devices 104 is not a limitation and that various spacingintervals may be used in the neutron detection system 100, with thespecific spacing chosen according to specific efficiency, accuracy, andsensitivity requirements of the given system for a known incidentneutron energy (i.e., neutron moderation is not perfectly linear betweendepth and energy).

Applicants have found that for a cylindrical-shape detector 102including 30 detection devices 104 spaced apart by 1 cm, with eachhaving a 6.35 cm radius and a moderator thickness of 0.5 cm a totaldevice efficiency of 30% is achievable.

In one embodiment, the volume of neutron moderation material may bedefined by a three dimensional shape. For example, the volume ofmoderating material surrounding the plurality of neutron detectiondevices 104 may include, but is not limited to, a cylinder, a sphere, acone, an ellipsoid, a cuboid or a hexagonoid. For instance, theplurality of neutron detection devices 104 may be embedded in acylindrical shaped volume of neutron moderating material. In anotherinstance, the plurality of neutron detection devices 104 may be embeddedin a spherically shaped volume of neutron moderating material. It willbe recognized by those skilled in the art that the symmetry of thevolume of moderation material is such that it allows for a systematicenergy-moderation relationship to be determined.

In a further embodiment, the volume of moderating material 109 may bedimensioned so as to substantially conform to the outer edges of the oneor more neutron detection devices 104 of the neutron detection system100. For example, as shown in FIG. 1G, the surface of a sphericallyshaped volume of neutron moderating material may conform to the surfaceof the detection volume, which may, but is not required to, serve as adefining boundary to the one or more neutron detection devices.

FIGS. 2A-2B illustrate schematic views of a detector 102 of thedetection system, in accordance with one embodiment of the presentinvention. In this embodiment, the detector 102 is designed with thedetection devices 104 arranged axially around a central moderator 128.In another embodiment, an outer moderator 127 surrounds the compactdetection devices 104 and core moderator 128. In a further embodiment,an electromagnetic lightproof shield 122 may surround the detectionvolume of the detector 102. In a further embodiment, a neutron andbackground radiation shield 126 may surround the entire structure. Thecompact neutron detection devices 104 may include coated semiconductorneutron detection devices or MSNDs. The moderators 127, 128 may include,but are not limited to, elemental, compounded or mixtures of plastic,polyethylene, high density polyethylene, carbon, graphite or water. Itis further noted that the detector embodiment of FIGS. 2A-2B may beformed in any geometrical shape described in the present disclosure,including, but not limited to, a cylinder, parallelepiped or conicalfrustum.

FIGS. 3A-3B illustrate schematic views of a detector 102 of thedetection system, in accordance with one embodiment of the presentinvention. In this embodiment, the detector 102 is designed with one setof detection devices 104 arranged axially around a central moderator128. In another embodiment, a middle moderator 127 surrounds the compactdetection devices 104 and core moderator 128. In a further embodiment,the compact neutron detection devices 104 are arranged around the middlemoderator 127, whereby an outer moderator 130 surrounds the compactdetectors 104, middle moderator 127 and core moderator 128. In a furtherembodiment, an electromagnetic lightproof shield 122 may surround thedetection volume of the detector 102. In a further embodiment, a neutronand background radiation shield 126 may surround the entire structure.The compact neutron detection devices 104 may include coatedsemiconductor neutron detection devices or MSNDs. The moderators 127,128, 130 may include, but are not limited to, elemental, compounded ormixtures of plastic, polyethylene, high density polyethylene, carbon,graphite or water. It is further noted that the detector embodiment ofFIGS. 3A-3B may be formed in any geometrical shape described in thepresent disclosure, including, but not limited to, a cylinder,parallelepiped or conical frustum.

FIGS. 4A-4B illustrate schematic views of a detector 102 of thedetection system, in accordance with one embodiment of the presentinvention. In this embodiment, the detector 102 is designed with one setof detection devices 104 arranged axially around a core moderator 128.In another embodiment, an outer moderator 127 surrounds the compactdetection devices 104 and core moderator 128. In another embodiment,neutron absorbing shield 132 (e.g., Cadmium shield) is arranged in theouter moderator 127 and around the core moderator 128 and compactneutron detection devices 104. The neutron absorbing shield 132 mayinclude, but is not limited to, elemental, compounded or mixtures ofcadmium, gadolinium, boron, lithium, indium, iron, lead, and mercury. Ina further embodiment, an electromagnetic lightproof shield 122 maysurround the detection volume of the detector 102. In a furtherembodiment, a neutron and background radiation shield 126 may surroundthe entire structure. The compact neutron detection devices 104 mayinclude coated semiconductor neutron detection devices or MSNDs. Themoderators 127, 128 may include, but are not limited to, elemental,compounded or mixtures of plastic, polyethylene, high densitypolyethylene, carbon, graphite or water. It is further noted that thedetector embodiment of FIGS. 4A-4B may be formed in any geometricalshape described in the present disclosure, including, but not limitedto, a cylinder, parallelepiped or conical frustum.

FIGS. 5A-5B illustrate schematic views of a detector 102 of thedetection system, in accordance with one embodiment of the presentinvention. In this embodiment, the detector 102 is designed with one setof detection devices 104 arranged axially around a core moderator 128.In another embodiment, a middle moderator 127 surrounds the compactdetection devices 104 and core moderator 128. In another embodiment, thecompact neutron detection devices 104 are arranged around the middlemoderator 127. In another embodiment, an outer moderator 130 surroundsthe compact detection devices 104, the middle moderator 127 and the coremoderator 128. In another embodiment, a neutron absorbing shield 132 isarranged in the middle moderator 127 and around the core moderator 128,placed between the compact neutron detectors 104 on the core moderator128 and compact neutron detectors 104 on the middle moderator 127.

FIGS. 6A-6B illustrate schematic views of a detector 102 of thedetection system, in accordance with one embodiment of the presentinvention. In this embodiment, the detector 102 includes a series oflow-power high-efficiency semiconductor thermal-neutron detectiondevices 104 with cylinders of plastic neutron moderator 106 placedbetween each pair of detection devices 104. In a further embodiment,each moderating region is bounded by a neutron absorber 120 so as toconfine neutrons to the moderator region in which the given neutronsfirst reach thermal energies. In a further embodiment, the detectiondevices 104 are segmented compact detection devices 104 includingmultiple detection elements 105. In an additional embodiment, the dataacquisition electronics 124 of the detector may be distributed such thateach segmented element 105 has a corresponding set of DAQ circuitryelements 124.

FIG. 7 illustrate a schematic view of a detector 102 of the detectionsystem, in accordance with one embodiment of the present invention. Inthis embodiment, the detector 102 is designed with the detection devices104 arranged axially around a central moderator 128. In anotherembodiment, an outer moderator 127 surrounds the compact detectiondevices 104 and core moderator 128. In a further embodiment, anadditional set of detection devices 104 are arranged vertically alongthe axial direction. In a further embodiment, an electromagneticlightproof shield 122 may surround the detection volume of the detector102. In a further embodiment, a neutron and background radiation shield126 may surround the entire structure. The compact neutron detectiondevices 104 may include coated semiconductor neutron detection devicesor MSNDs. The moderators 127, 128 may include, but are not limited to,elemental, compounded or mixtures of plastic, polyethylene, high densitypolyethylene, carbon, graphite or water. It is further noted that thedetector embodiment of FIG. 7 may be formed in any geometrical shapedescribed in the present disclosure, including, but not limited to, acylinder, parallelepiped or conical frustum.

FIG. 8 illustrate a schematic view of a detector 102 of the detectionsystem, in accordance with one embodiment of the present invention. Inthis embodiment, the detector 102 is a substantially spherical neutrondetector 102 with compact detection elements 104 arranged radially in amoderator 106. In one embodiment, the compact neutron detectors 104 arearranged upon removable shells 136 of moderator 106. The moderatorshells 106 may be composed of, but are not limited to, elemental,compounded or mixtures of plastic, polyethylene, high densitypolyethylene, carbon, graphite or water.

FIGS. 8A-8B illustrate a schematic view of a detector 102 of thedetection system, in accordance with one embodiment of the presentinvention. In this embodiment, the detector 102 is a substantiallyspherical neutron detector 102 with compact detection device 104arranged radially in a moderator where the compact neutron detectiondevices and arranged in removable moderator plugs 137. In this regard,the moderator plugs 137 may be selectably inserted radially into a largemoderator mass 138 via the moderator plug receptacle 140. The moderatorplugs 137 and large moderator mass 138 may be composed of, but are notlimited to, elemental, compounded or mixtures of plastic, polyethylene,high density polyethylene, carbon, graphite or water.

In another embodiment, the detection system 100 may include two or moredetectors 102 arranged substantially orthogonally to one another. Forexample, the detection system 100 may include a first cylindricaldetector 102 and a second cylindrical detector, which are arranged suchthat their axial dimensions are perpendicular to one another. By way ofanother example, the detection system 100 may include a firstcylindrical detector 102, a second cylindrical detector 102, and a thirdcylindrical detector 102, which are arranged such that their axialdimensions are mutually orthogonal to one another.

Referring now to FIGS. 1I through 1N, one or more of the neutrondetection elements 105 of one or more of the neutron detection devices104 may include detection elements 105 having a geometrical shape. Forexample, a neutron detection element 105 may include, but is not limitedto, a solid state neutron detection element 105 having, from a top view,the shape of a circle, a portion of a circle, a hexagon, a rectangle(e.g., a square), a ring, an ellipse, or a triangle. For instance, asshown in FIG. 1I, the neutron detection devices 104 may contain a numberof quarter-circle shaped neutron detection elements 105. In anotherinstance, as shown in FIG. 1J, the neutron detection devices 104 maycontain a number of square shaped neutron detection elements 105. Inanother instance, as shown in FIG. 1K, the neutron detection devices 104may contain a number of hexagonal shaped neutron detection elements 105.In another instance, as shown in FIG. 1L, the neutron detection devices104 may contain a number of circular shaped neutron detection elements105. In an additional instance, as shown in FIG. 1M, the neutrondetection devices 104 may contain a number of concentric ring shapedneutron detection elements 105. Further, as shown in FIG. 1N, theneutron detection devices 104 may contain a number of neutron detectionelements 105 having a sectioned concentric ring shape. It should berecognized by those skilled in the art that the use of the describedshapes for the neutron detection elements 105 is not a limitation andthat the implemented neutron detection elements 105 of the neutrondevices 104 may have a variety of geometrical shapes.

Moreover, it should be noted that the individual neutron detectionelements 105 may have a substantially three dimensional character. Forexample, as shown in FIG. 1H, the volume of a detection element 105(e.g., hexagonal shaped element 105) may extend along the axialdirection of the detection device 104 below the planar surface of thedetection device 104. It is this entire elemental volume (i.e., a voxel)that serves as the neutron detection (e.g. via neutron capture,neutron-induced fission, or scatter) element 105. The volumetric extentof a given three dimensional element 105 is fixed by: 1) the arealcontact size used and 2) the device thickness, as illustrated in FIG. 1Hrespectively.

Referring again to FIGS. 1A through 1G, the plurality of the neutrondetection devices 104 and the surrounding neutron moderating material109 may be engineered such that the overall neutron detector 102 issubstantially defined by a three dimensional shape. For example, theshape of the neutron detector 102 may include, but is not limited to, acylinder, sphere, an ellipsoid, a cone, a cuboid, or a hexagonoid. Itwill be recognized by those skilled in the art that the choice of shapeof the neutron detector 102 may depend on the specific purposes of theneutron detection system 100. The applicants have found that acylindrically shaped detection volume is preferred in analyzing incidentneutron characteristics when the incident neutrons have a preferentialdirection or of parallel incidence. It has been further found by theapplicants that a spherically shaped detection volume 110 may bepreferred in analyzing impinging neutron properties of isotropicneutrons.

As illustrated in FIGS. 9A through 9C the system 100 may include controlassembly 902 and a moderator assembly 904 configured for containing atleast a portion of the system 100. In an embodiment, the controlassembly 902 may include the display 117 and at least one user inputdevice 119. The control assembly 902 may be configured for holding oneor more detection device 104, each including at least one detectionelement 105. In further embodiment, the control assembly 902 may beconfigured to hold a plurality of detection devices 104, each includinga plurality of detection elements 105. The detection devices 104 mayfurther include a coating material 908 such as, but not limited to,radiation shielding material, absorbing material, electromagnetic lightshielding material, and the like.

Each detection device 104 may be configured for removably coupling tothe control assembly 902 via at least one connector 910. In oneembodiment, the connector 910 may include one or more conductive pinsconfigured to plug into sockets within the control assembly 902.Alternatively, the connector 910 may include at least one female socketconfigure for receiving male pins of the control assembly 902. Theconnectors 910 of the detection devices 104 are not limited toconductive male/female connectors. It is contemplated that theconnectors 910 may include alternative means of transferringinformation, such as wireless transmitters, receivers, and/ortransceivers.

The control assembly 902 may be further configured for removablycoupling to at least one moderator assembly 904. The moderator assembly904 may be configured for holding a volume of moderator material 109.The moderator assembly 904 may be further configured for receiving thedetection devices 104 when coupled to the control assembly 902. In anembodiment, the moderator assembly 904 may include one or more slots 906or alternative structural features configured for receiving thedetection devices 104.

In some embodiments, the control assembly 902 may be configured forremovably coupling to a plurality of moderator assemblies 904 allowingthe moderator assemblies 904 to be selectively interchanged. In anembodiment, a first moderator assembly 904 may be interchanged with asecond moderator assembly 904 at a predetermined or selected interval oftime or use. In another embodiment, each moderator assembly 904 may beconfigured for holding a different volume of moderator material 109. Forexample, the moderator assembly 904 holding a first volume of moderatormaterial 109 may be interchanged with another moderator assembly 904holding a selected volume of moderator material 109.

FIG. 10 illustrates a schematic view of a detector 102 of the detectiondevice 100 coupled to various control and data acquisition circuitryelements 1002-1014. The circuitry elements 1002-1014 may correspond toswitching circuitry, shaping circuitry, A/D circuitry, FPGA circuitry,mstFPGA circuitry, power circuitry, and communication circuitryrespectively.

In a further embodiment, each of the plurality of neutron detectiondevices 104 may be communicatively coupled to the one or more processingelements 110 of the control system 108 via a data coupling (e.g.,wireline data coupling or wireless data coupling). For example, each ofthe plurality of neutron detection devices 104 may transmit neutrondetection response data to the one or more processors 110 of the controlsystem 108 via a data connection. In another example, each of theplurality of neutron detection devices 104 may transmit neutrondetection response data to a response detection database maintained inthe memory 112 of the control system 108 via a data connection. In thisregard, the neutron response data may be maintained in the memory 112and retrieved at a later time by the one or more processing elements110, allowing the system 100 to perform the various steps of the presentinvention at any time following interrogation of a given spatial regionfor neutron source existence and/or identification.

For the purposes of the present disclosure, the term “processingelement” is broadly defined to encompass any device having dataprocessing and/or logic capabilities. In one embodiment, the one or moreprocessing elements 110 of the control system 108 may include, but arenot limited to, one or more processors. In a further embodiment, the oneor more processors are configured to execute program instructions from amemory medium 112. In this sense, the one or more processors may includeany microprocessor-type device configured to execute software algorithmsand/or instructions. In one embodiment, the one or more processors mayconsist of a desktop computer or other computer system (e.g., networkedcomputer) configured to execute a program configured to operate thesystem 100, as described throughout the present disclosure. It should berecognized that the steps described throughout the present disclosuremay be carried out by a single computer system or, alternatively,multiple computer systems.

Moreover, different subsystems of the system 100, such as the displaydevice, the user interface device, individual detection devices, and thelike, may include processing elements suitable for carrying out at leasta portion of the steps described above. Therefore, the above descriptionshould not be interpreted as a limitation on the present invention butmerely an illustration.

In one aspect, the one or more processing elements 110 of the controlsystem 108 are configured to determine one or more energycharacteristics of the neutrons 103 impinging on the detector 102. Inone embodiment, the one or more processing elements 110 are configuredto execute a set of program instructions suitable for carrying out asummation of one or more detection events as a function of one or morecoordinate axes or convolution of axes in order to determine one or moreenergy characteristics of neutrons 103 impinging on the detector 102. Ina further embodiment, the control system 108 may determine a neutronsource type utilizing one or more of the determined one or more energycharacteristics of the impinging neutrons 103. In another embodiment,the control system 108 may determine a dose of a neutron sourceutilizing one or more of the determined one or more energycharacteristics of the impinging neutrons 103.

Applicants again note that the spatial position, within the moderatingvolume 109, that a neutron reaches thermal energy and is subsequentlydetected by a thermal neutron detector 102 is correlatable to thekinetic energy of neutrons 103 incident from a neutron source 101. It isfurther noted that in one or more of the various geometries describedpreviously herein (e.g., parallelepiped geometry, cylindrical geometry,spherical geometry and the like) the spatial positions of the variousnumber detected neutron capture events (e.g., the depth of the neutrondetection device that is most frequently triggered) may be correlated tothe energy spectrum of the incident neutrons. In turn, the controlsystem 108 may determine a characteristic (e.g., source-type, dose, andthe like) of an interrogated neutron source 101 based on the determinedenergy spectrum of the incident neutrons.

Applicants further note that the various embodiments of the one or moredetectors 102, detection devices 104, and the detection elements 105described throughout the present disclosure provide for the first time atrue three-dimensional characterization of neutron thermalization in amoderating medium. The inclusion of characterization along multiple axesallows the system 100 of the present invention to generate uniqueneutron response functions, which aid in neutron energy characteristicanalysis. Specifically, the present invention allows for the tracking ofneutron thermalization to less than 1 cm³. It is further noted thepresent invention allows for the thermalization tracking withoutsignificant perturbation to the thermalization process. In addition, thepresent invention allows for this resolution in a portable measurementdevice configuration. Further, the present invention provides a highintrinsic efficiency to fast neutrons, such as bare spontaneous fissionemitters (e.g., ²⁵²Cf). The inclusion of characterization alongadditional axes allows the system 100 of the present invention togenerate unique neutron measurement information, which improves neutronenergy characteristic analysis over the prior art. Moreover, while thefollowing description focuses on a few specific geometries, it is notedthat the foregoing description of analysis procedures may be applied inthe context of all of the configurations and geometries describedpreviously herein.

In one embodiment, the control system 108 may generate a source“signature” or “fingerprint” utilizing the aggregated position dependentneutron thermalization data along one or more coordinate axes (e.g.,x-y-z in Cartesian coordinate system; r, θ, φ in spherical coordinatesystem; r, z, φ in cylindrical coordinate system, and the like) withinthe detector moderating volume 109. For example, the control system 108may aggregate the responses measured by the multiple detection elements105 of the detection devices 104 of the detector 102 in order togenerate a source signature for a given neutron source measurement.

In another embodiment, the one or more processing elements 110 maygenerate one or more detector response libraries and maintain the one ormore detector response libraries in the memory 112 of the control system108. In some embodiments, the response library may be generated via aseries of empirical processes. For example, the control system 108 maystore various sets of normalized detector response data acquired by thesystem 100 during measurement of known neutron sources at known spatialpositions and environments relative to the system 100. In otherembodiments, the response library may be generated via simulation. Forexample, as shown in FIG. 11, Monte Carlo based calculations 1100 may beused to model the response of the detector 102 to various neutronsources (e.g., monoenergetic sources). Similarly, FIG. 12 depicts aseries of Monte Carlo based calculations 1200 illustrating the predictedresponse of a given detector for a number of incident neutron energies(e.g., thermal neutrons energies through 10 MeV) as function ofdetection location within the detector. In this regard, the implementedmodel may be tuned to the specific structural characteristics of thedetector 102 of the system 100. In this regard, the modeled responsefunctions may take into account the spacing of detector devices 104, thethickness(es) of moderating material between various detector devices104, the radius of detector devices 104, the depth of detector devices104, the moderator type, the variability of the moderator make upthroughout the detector 102, the absorber type, and the variability ofthe absorber make up throughout the detector 102 and etc.

In another embodiment, the one or more processing elements 110 areconfigured to compare the generated source signature to a detectorresponse library 115 stored in the memory 112 of the control system 108.In this regard, the one or more processing elements 110 may compare theneutron detection curves (generated by aggregating the detection countsfrom each of the detection elements 105 of each of the detector devices104) generated by an interrogated source 101 (i.e., an unknown potentneutron source) to the various response curves stored in the detectorresponse library 115. The comparison between collected response data inthe detector 102 and the response library 115 may be carried out inanyway known in the art.

In another embodiment, the comparison between collected response dataand the response library 115 may be carried out utilizing across-correlation technique. In a first step, the number of relativeneutrons (intensity) reaching thermal energy (on average) is collectedas a function of one-, two-, or three-dimensional position within themoderating volume 109, and binned along one or more coordinate axesand/or one or more convolutions of the coordinate axes. In second step,the number of relative neutrons (intensity) reaching thermal energy (onaverage) originating from known sources and source configurations arecalculated as a function of one-, two-, or three-dimensional positionwithin the moderating volume 109, and binned along one or morecoordinate axes and/or one or more convolutions of the coordinate axes.In a third step, the binned quantities from the first step are comparedto the binned quantities of the second step by measuring a degreecommonality (e.g., a score of commonality is assigned for eachcomparison) for the each of the known source/source configurations. In afourth step, the matching neutron source and configuration is identifiedutilizing the highest degree of commonality found in step 3.

In the case of a cylindrical geometry, such as that depicted in FIG.1C-1E, the response or intensity of neutron counts from the detectordevices 104 (or detection devices 105 in a segmented or pixelatedconfiguration) as a function of the axial depth in the moderatingdetector 102 is a function of the incident neutron spectrum. In thisregard, lower energy spectral neutrons are preferentially detected inthe first few detector devices 102, while higher energy spectralneutrons tend to penetrate deeper along the axial length of the detector102, and, resultantly are detected in “deeper” detection devices 102.Applicants note that one complicating factor is the likely presence ofcosmic-ray induced spallation neutrons (or some othermasking/convoluting neutron source), which may also create a uniqueresponse in the detector 102. In order to determine the magnitude of theneutron source 101 strength in the presence of neutrons associated withthe cosmic background, as well as determine the source's identity, thesource's environment, or local configuration of the source 101,cross-correlation analysis may be utilized. It is further noted thatsource strength may also be implemented in settings where cosmicbackground neutrons are not present. For the purposes of the presentdisclosure, “cross-correlation” represents a measure of similaritybetween two or more waveforms and is used for pattern recognition. In afurther embodiment, the control system 108 may apply a normalizedcross-correlation procedure with an output score or coefficient (e.g.,Pearson product-moment correlation coefficient). The normalizedcross-correlation procedure of the present invention may includeconvolving a measured energy (E) and a reference response (R) of thedetector 102 by summing the product of the normalized measured andreference responses from each data point (i.e., signal from the i^(th)detector along some coordinate axis or the signal from some i^(th) andj^(th) detector along two or more coordinate axes or any combination ofdetectors that yields a unique signature that may be compared against inthe reference library). It is further noted that normalization isaccomplished by subtracting the mean from the measured or referenceresponse and dividing by the standard deviation of the mean. Theresulting normalized functions are multiplied by each other and summed.The result is a cross correlation score for a given “guessed” referenceresponse R. The cross-correlation score for a given response R is givenby:

${{Cross}\mspace{14mu}{Correlation}} = {\frac{1}{N - 1}{\sum\limits_{1}^{n}{\frac{\left( {E_{i} - \overset{\_}{E}} \right)}{\sigma_{E}}*\frac{\left( {R_{i} - \overset{\_}{R}} \right)}{\sigma_{R}}}}}$

where E_(i) is the experimentally measured response function for thei^(th) diode; Ē is the mean of the measured response data; R_(i) is a“guessed” response based upon reference data; R is the mean of theguessed response data; σ_(E), σ_(R) are the standard deviations of thetwo functions; and N is the number of detector devices 104 (e.g.,diodes) in the detector 102.

In a further embodiment, in order to determine the source type andsource magnitude, trial spectrometer responses R are generated frommodeled reference spectra (e.g., MCNPX reference spectra). First, aresponse function for a particular source (e.g., ²⁵²Cf) is selected. Theresponse of the detector 102 to this source is added to the cosmicresponse starting with the source 101 being some small fraction of thecosmic background (say 1%) and a cross-correlation factor is calculated.The source 101 magnitude is incremented, producing a new trial responseR and the cross-correlation is calculated again. This process iscontinued up to some arbitrarily large amount of source strengthcompared to cosmic. After determining cross-correlation factors for oneassumed source, the process is repeated for a different (e.g. AmBe)source. The result is a series of cross-correlation factors as afunction of source type and source strength. The highestcross-correlation factor predicts the best match of source type andstrength to the experimental measured E.

In another embodiment, the incident neutron spectra may be determined byunfolding the measured data in light of the detector response functions.In this regard, any unfolding technique known in the art may be utilizedin conjunction with the detector response library 115 to deduce one ormore energy characteristics associated with the neutrons 103 impingingon the detector. Applicants note that in one embodiment in executing theone or more unfolding process the control system 108 may utilize as aninput a measurement matrix N (as measured by the various detectionelements 105) and a response matrix M (stored in the memory 112 of thecontrol system 108). In this regard, the control system 108 may invertthe relationship given by N=RI in order to determine the incidentneutron spectra I.

For instance, unfolding techniques may be used to determine the energydistribution of the impinging neutrons 103, the peak energy of theimpinging neutrons 103, the high-energy tail of the neutron 103 energydistribution. Utilizing these or other energy characteristics, thecontrol system 108 may then deduce the unknown interrogated neutronsource 101. It is recognized herein that various mathematical andmodeling principles may be implemented in order to “unfold” the measureddata in light of the detector response functions. For example, theunfolding operations may include, but are not limited to, inverse MonteCarlo techniques and regularization techniques.

In one implementation, in a cylindrical neutron detection system 100, asshown in FIG. 1E, in a setting where incident neutrons impinge on thedetector 102 in a substantially parallel manner (i.e., in axialdirection), the control system 108 of the neutron detection system 100may be calibrated in terms of depth using a library of detectorresponses for multiple neutron sources (e.g., acquired throughmeasurement of known sources (e.g., monoenergetic, bare spontaneousfission (252-Cf), moderated spontaneous fission, α,n sources (AmBe),etc.) or detector response modeling), as described above. After buildingup appropriate calibration data sets, and thus correlating thepenetration depth with actual incident neutron energy using the detectorresponse library 115, the cylindrical neutron detection system 100 maythen be used to measure quantities proportional to or correlatable withthe energy of incident neutrons. Moreover, by comparing the measuredpenetration depth data (flux vs. depth or intensity vs. depth) to thecalibration data from the neutrons from the known neutron sources (fluxvs. depth or intensity vs. depth for known energy), a spectrum (flux vs.energy or intensity vs. energy) can be deduced and it is possible tothen further deduce the type of neutron source and/or dose using themethods described above. It is further contemplated that for thepurposes described in the present disclosure the terms “flux” and“intensity” are substantially interchangeable as intensity representsthe total number of neutrons that have impinged at a given detectorelement, whereas flux represents the total number of impinging neutronsper unit area per unit of time. It should be recognized by those skilledin the art that an intensity value is readily converted to a flux valueand vice-versa based on the length of time of a given measurement.

In another implementation, a cylindrically symmetric shaped neutrondetection system 100, as shown in FIG. 1E, may be utilized to measurethe energy spectrum of incident neutrons impinging on all faces of theneutron detection system 100. One skilled in the art will appreciatethat in a cylindrical geometry, assuming isotropic incidence ofimpinging neutrons 103, the depth at which a number of detected neutroncapture events is maximum (i.e., the depth of the neutron detectiondevice that is most frequently triggered) can be correlated with theenergy of the incident neutrons 103. To accomplish the depth resolutionfor isotropic incidence on the cylindrical geometry, both a radial andaxial dependence of intensity must be determined. While the axialdependencies may be determined in a manner similar to that described inthe preceding description, the radial dependence may be formed by anumber of neutron detection elements 105 (e.g., elements 105 shown inFIG. 1E), which create a pixilated or segmented effect in each detectordevice 104. For example, radial dependence may be accomplished utilizinga hexagonal array arrangement (see FIG. 1E), a dot array arrangement(see FIG. 1L), a square array arrangement (see FIG. 1F), a concentricring arrangement (see. FIG. 1M). Each of these arrangements allow forthe control system 108 to determine the off-axis position of a neutroncapture event in a given detector device 104. In a manner described inthe preceding section, both radial and axial directions may requirecalibration by known neutron sources, either through calibrationmeasurements or calibration modeling, in order to provide themoderator-energy correlation.

Applicants note that it is desirable to provide a detector 102 having aradius larger than the mean free path of the most energetic incidentneutron in order to reduce the likelihood of the neutron passing throughto the opposite side of the detector device 104, thereby polluting theintensity measurement.

In another implementation, a rectangular or square shaped neutrondetection system 100, as shown in FIG. 1F, may be utilized to measurethe energy spectrum of parallel incident neutrons impinging on thedetector 102. As in the case for cylindrical geometry, the controlsystem 108 of the neutron detection system 100 may be calibrated interms of depth using multiple known neutron sources (e.g., monoenergeticneutron sources), as described above. After building up appropriatecalibration data sets, and thus correlating the penetration depth withactual incident neutron energy using the detector response library 115,the rectangular neutron detection system 100 may then be used to measurethe energy spectrum of incident neutrons. Again, by comparing themeasured penetration depth data to the calibration data from theneutrons from the known neutron sources (or modeling results), aspectrum can be deduced, allowing for the deduction of the type ofneutron source 101.

In another implementation, a spherically symmetric shaped neutrondetection system 100, as shown in FIG. 1G, may be utilized to measurethe energy spectrum of parallel incident neutrons impinging normal toany tangent on the sphere. One skilled in the art will appreciate thatin the spherical geometry, assuming parallel incidence of impingingneutrons, the radial depth at which a number of detected neutron captureevents is maximum in less than one hemisphere, is correlatable to theenergy of the incident neutrons. To accomplish the depth resolution forparallel incidence in the spherical geometry, the radial, phi, and thetadependence of the intensity may be determined. To provide the greatestspectroscopic clarity, the sphere radius should be greater than themacroscopic mean free path of the most energetic neutron to be detected,but not so large that the most energetic neutrons terminate outside thequarter radius. Detection element 105 pixilation may be formed asdescribed in preceding description. It is further noted, that thespherically shaped neutron detection system 100 may be implemented tomeasure the energy spectrum of parallel incident neutrons (i.e.,neutrons moving substantially along the polar axis of sphere) on thedetector 102.

In another implemenation, a spherically symmetric shaped neutrondetection system 100 may be implemented to measure the energy spectrumof omnidirectional neutrons 103. One skilled in the art will appreciatethat in a spherical geometry, assuming omnidirectional incidence ofimpinging neutrons, the radial depth at which a number of detectedneutron capture events is maximum (i.e., the depth of the neutrondetection device that is most frequently triggered) may be correlatedwith the energy of the incident neutrons. The volume of elements andmoderator-energy correlation calibration may be completed as describedabove.

It is further contemplated that the detection system geometry andsymmetry described above may be extended to the conical, pyramidal, andother rotationally and/or mirror plane invariant symmetries in order toobtain a coordinate dependence of the intensity from which incidentneutron energy may be determined.

In another embodiment of the present invention, the one or moreprocessing elements 110 are configured to execute a set of programinstructions suitable for carrying out a dose determination algorithm inorder to determine a dose of neutrons 103 impinging on the detector 102.In this regard, the neutron detection system 100 of the presentinvention may be configured as a dosimeter (i.e., REM meter).

In one embodiment, the detection system 100 may be configured as aneutron dosimeter by utilizing volumetric identification of fast neutronthermalization in the context of forming a semiconductor-basedBonner-like neutron detector, such that the entire moderating volume issampled locally for thermal neutrons. Such volumetric resolution ispossible through the layering of weakly perturbing and pixilated highthermal efficiency semiconductor neutron detection devices 104 into aneutron moderator 109. The use of multiple detection devices 104provides detailed information concerning the spectral characteristics ofthe neutron field, critical to determining dose conversion factors whichare strongly dependent upon incident neutron energy.

Applicants note that “dose” may be determined via one of more dosecalculation algorithms executed by the control system 108. In oneembodiment, since the response of each detection element 105 is uniqueand varies throughout the detector volume of the detector 102, theresponse of the various elements 105 may be unfolded in order to providean estimate of the incident neutron 103 spectrum. In turn, the incidentneutron spectrum may be converted to dose via a flux-to-dose doseequivalent relationship. In another embodiment, the control system 108may superimpose the linear combinations of the detector responsefunctions to duplicate the unique flux-to-dose conversion function. Theresponse of each detector element 105 may be multiplied by the linearcombination coefficients and summed to provide their individualcontributions to the total dose. In yet another embodiment, a thirdalgorithm may make use of the fact that neutron spectra in applieddosimetry environments are typically perturbations on a characteristicspectrum of fast neutrons around 1-10 MeV, a slowing down region in the1 eV to 1 keV range and a thermal neutron component. In this regard, thesystem 100 may utilize a library of stored neutron spectra along withthe corresponding dose equivalents for these spectra. The control system108 may determine the most likely neutron spectral field (and thus dose)by a cross-correlation evaluation of the individual detection element105 responses to that of the library of responses from the assumedspectra.

In one embodiment, the neutron detection system 100 may be configured toresolve ambient neutron dose equivalent spanning the thermal to 15 MeVrange. In one embodiment, the neutron detection system 100 maysimultaneously count thermalized neutrons by weakly perturbing and highthermal efficiency solid state neutron detector devices 104. It is notedthat the utilization of multiple detector devices 104 and moderatormaterial 109 arranged along an axis of symmetry (e.g., long axis of acylinder) with known neutron-slowing properties allows for theconstruction of a linear combination of responses that approximate theambient dose equivalent.

Those skilled in the art should recognize that the operational quantitydevised by the International Commission on Radiation Units andMeasurement (ICRU) for operational radiation field measurements is theambient dose equivalent, denoted H*(10) and defined as the effectivedose equivalent at a point of interest in a radiation field which wouldbe generated at a 10 mm depth in a superimposed tissue-equivalentsphere. For the case of monoenergetic neutrons at energy E, the ambientdose equivalent is then given by:H*(10)=Φ_(E) h _(cc,E)

where Φ_(E) is the mono-energetic neutron fluence and h_(cc,E) is aneutron dose-equivalent conversion value specific to the energy of theincident neutrons that accounts for both the quantity of energydeposition as well as the corresponding RBE implications. It is notedherein that detailed knowledge of the energy dependent ambient neutrondose equivalent and spectral fluence is necessary for accuratedosimetric calculations. Note that h_(cc,E) is a highly nonlinearfunction in energy in which relatively low equivalent dose per neutron(˜10 pSv-cm2) is observed at energies below 10 keV, followed by a nearlytwo order-of-magnitude increase (−600 pSv-cm2) between 10 keV and 1 MeV.

Due to the ability of the system 100 to determine the thermalization ofneutrons volumetrically (<1 cm3) along one or more geometric coordinateaxes in real-time, the system 100 may be used to accurately accommodatethe non-linear shape of the ambient dose equivalent conversion curve,such that the neutron energy correction factor can be adjustedelectronically. For the case of free neutrons travelling in parallel,this task can be accomplished by stacking high thermal efficiencydetection devices (or comparable weakly volumetric perturbing detectiondevices), into an axially symmetric moderator geometry, like that thedetector 102 having right cylindrical geometry shown in FIG. 13A, asdescribed throughout the present disclosure. In an alternativeembodiment, the detection devices 104 may include detection devicesbeing comparably weakly perturbing to the overall volume and having atleast one-dimensional position sensitivity. In the case of the detector102 depicted in FIG. 13A, it is assumed that the neutrons are paralleland incident on the front face of the cylinder as shown in FIG. 13A. Infurther embodiments, as discussed previously herein, the detector 102may be covered in both ¹¹³Cd and a concentric moderator to preventthermal and epi-thermal neutrons, incident from the sides or back frombeing detected (i.e., a camera geometry) within the detector volume.Conversely, if there were very few neutrons and they were incident fromall directions, a spherical geometry with radial dependence may beimplemented.

In one embodiment, a one-dimensional axial binning scheme is presentedin the form of the histogram 1302 in FIG. 13B, representative ofdetected neutrons 1312 and is unique to the energy and intensity of thegiven incident neutron source 101 (unmoderated ²⁵²Cf in the caseillustrated). The thickness/volume of the detector 102 is defined by thedetection devices 104 and any necessary electronics that are positionedin the neutron path (e.g., preamplifiers, fiberglass boards, etc.). Inone embodiment, specifications for thermal efficiency and large detectorarea may be met utilizing the indirect conversion MSNDs describedpreviously herein. In one embodiment, the MSND-based devices may utilizethe thermal neutron capture with ⁶Li (938 barns) to produce at leasttwenty percent thermal neutron detection efficiency.

The minimal perturbation of each detector to the moderation process,combined with the high thermal-efficiency of each detection device 104,permits the investigation of an individual device's output with respectto the corresponding degree of observed moderator penetration. Energydependence considerations allow for the delivery of distinct efficiencyvs. energy curves as a function of moderator thickness that closelyresembles the acquisition from collections of Bonner sphereconfigurations. The availability of n simultaneous measurements from ndetectors with unique Bonner-like response functions permits revision ofits REM meter's dose response curve to:

M = ∫₀^(∞)Φ₀(E)f(d_(cc, 1)(E)  …  , 𝕕𝕕_(cc, n)(E))𝕕E

where the single detector response curve of a conventional REM meter isreplaced by a function of multiple response curves, f, to permit moreaccurate matching to h_(cc,E). In one embodiment, a linear combinationof the individual Bonner-like response functions may be used to forcethe dosimeter's (i.e., the detector 102) overall response function tomimic the shape of the provided absorbed dose-equivalent curve such thatƒ(d _(cc,1)(E), . . . ,d _(cc,n)(E))=h _(cc)(E)=g ₁ d _(cc,1) +g ₂ d_(cc,1) + . . . +g _(n) d _(cc,n)

where g_(i) is the gain corresponding to the ith detector's responsefunction, d_(cc,i). Applicants note that it is this gain that allows forthe electronic matching to any dose equivalent curve. In anotherembodiment, a collection of measurements from m monoenergetic sourcesspanning the pertinent energy range may then be used to populate an m byn matrix, B, where the corresponding h_(cc,E) values populate a m by 1column matrix, y. As such, the discrete Fredholm equation may beexpressed as:y _((m,1)) =B _((m,n)) G _((n,1))

where G is the gain matrix containing n optimal multiplier values(g₁-g_(n)). Assuming an overdetermined system, identification of theoptimal gain values is now accomplished by minimization of a “cost”function, selected for this case to be the sum of the square of theresiduals:J=[y _((m,1)) −B _((m,n)) G _((n,1))]^(T) R _((m,m)) ⁻¹ [y _((m,1)) −B_((m,n)) G _((m,1))]

where R is a diagonal matrix populated by the desired weights, for thiscase the inverse square values of y. Assuming B is invertible:G _((n,1)) =[B _((n,m)) ^(T) R _((m,m)) ⁻¹ B _((m,n))]⁻¹ B _((n,m)) ^(T)R _((m,m)) ⁻¹ y _((m,1))

Once the gain values are determined, the ambient dose equivalent due toa cumulative detector response can be determined from a series ofbackward substitutions as:H*(10)=C×[d ₁ g ₁ +d ₂ g ₃ + . . . +d _(n) g _(n)](mrem)

where d_(i) is the number of counts measured on the ith detector. Inthis regard, the control system 108 may apply this relationship todetermine the ambient dose equivalent using neutron counts as measuredby the various detector devices 104 as an input. Applicants further notethat following model identification, the dose equivalent, or dose-rate,for any ambient measurement/spectra can be calculated from the samelinear combination technique now performed on the total counts measuredby each detector.

In another embodiment of the present invention, the one or moreprocessing elements 110 of the control system 108 are configured toexecute a set of program instructions suitable for determining one ormore characteristics associated with the neutrons 103 impinging on thedetector 102. In one embodiment, reference response functions may bestored in memory 112 of the control system 108. In one embodiment, theresponse functions may include a reference for spectral shape (i.e.,neutron intensity dependence along one or more coordinate axes). Inanother embodiment, the response function may include a reference forneutron magnitude (e.g., raw neutron fluence, flux dosimetric magnitude,and the like). In a first step, the control system 108 may normalizeboth reference and measured responses for the purpose of thecross-correlation or desired template matching analysis method.Applicant notes that the previously described cross-correlation approachmay be applied herein. Then, after a best fit has been determined, amagnitude (e.g., dose, dose rate, fluence or flux) to total countsrelationship of the reference may be used to provide the incident dose,dose rate, fluence or flux for the integral number of counts detected inthe given measurement by the detector 102.

FIGS. 14A-14F illustrate a Variable Moderator Thickness (VMT) NeutronSpectrometer 1400 contained in a compact and portable form. Thespectrometer may include a thermal neutron detector 1414 such as, butnot limited to, thin-film coated semiconductor neutron detectors,microstructured semiconductor neutron detectors, gas-filled neutrondetectors, coated wall neutron detectors, coated fin neutron detectors,and the like. In one embodiment, the thermal neutron detector 1414 mayinclude a microstructured semiconductor neutron detector, such as thoseproduced by the Semiconductor Materials and Radiological Technologies(S.M.A.R.T.) Laboratory at Kansas State University. The neutron detector1414 relies on neutron moderator material 1418 between it and theneutron source. The thickness of moderator material 1418 present in theneutron moderation section 1416 may be variable. In an embodiment, thethickness may be controlled by an actuator, such as an onboard motor andpiston system 1404A, 1404B or another on board control system housed inan inert casing such as, the outer shell described herein.

As moderator material 1418 is added or removed from the neutronmoderation section 1416 the number of neutron scatters that occur withinthe neutron moderator material 1418 changes. The more moderator material1418 is present within the neutron moderation section 1416, the morescatters that will occur and therefore higher energy neutrons will bedown scattered into the thermal energy ranges. This allows for detectionof high energy incident neutrons. If the energy of neutrons emitted by asource is unknown, then an investigation can be made by varying theamount of moderator material 1418 in the neutron moderation section 1416and taking several counts. The number of counts recorded at eachiteration may be tallied into calibrated energy bins and as moreiterations are made, a spectrum of neutron energies may be resolved.

The spectrometer 1400 may be partially or entirely contained in an outershell 1402A, 1402B, 1406, 1408, and 1416. The strength of the shellmaterial may allow for transport of the device in harsh environments.For example, the outer shell 1402A, 1402B, 1406, 1408, and 1416 thatserves as the container for most of the functioning neutron spectrometercan be manufactured from materials that are resistive to corrosion,strong, low cost, and/or readily available including, but not limitedto, aluminum, graphite, titanium, stainless steel, and the like. In someembodiments, the materials may have low total neutron cross-sections. Alow total neutron cross-section may allow for the greatest number ofneutrons to stream through the shell, improving counting statistics andaccuracy of an investigation. Another advantage of a tow total neutroncross-section is the reduction of (n,X) reactions and therefore lessnoise in a neutron detector 1414. The outer shell may contain moderatormaterial 1418, moderator material drive systems 1406 neutron shieldingapparatuses 1410 and 1412, and the neutron detector 1414. In anembodiment, the shell 1402A, 1402B, 1406, 1408, and 1416 may becompartmentalized into three main chambers including, the neutronmoderation section 1416, the neutron detector and moderator drivecomponent housing 1408 and the excess moderator reservoir 1406. Thethree compartments may be sealed together with the neutron moderationsection 1416 and the excess moderator reservoir 1406 connected through apipe in order to allow for moderator flow from one to the other.

Referring to FIG. 14D, end caps 1402A, 1402B may be disposed at thefront and rear of the neutron spectrometer device. The end caps 1402A,1402B primarily serve as a means of sealing the neutron moderationsection 1416 and the excess moderator reservoir 1406, thus retaining themoderator material 1418. In an embodiment, the end caps 1402A, 1402B aredesigned to allow for optimum streaming of incident neutrons of allenergies. The end caps 1402A, 1402B may serve an additional purpose ofrestraining the moderator pistons 1404A, 1404B found in both the neutronmoderation section 1416 and the excess moderator reservoir 1406.

The moderator pistons 1404A, 1404B serve as the driving force that movesmoderator material 1418 to and from the excess moderator reservoir 1406and the neutron moderation section 1416. Depending on viscosity of theneutron moderator 1418, it may only be necessary to drive one moderatorpiston 1404A, 1404B since force may be transferred pneumatically to thesecond moderator piston 1404A, 1404B. Several methods of pneumaticallytransferring force include, but are not limited to, pumping air or othernon-neutron-attenuating materials behind a moderator piston 1404A,1404B, pulling a vacuum behind a moderator piston 1404A, 1404B, a wormscrew and motor drive system, or a magnetic coupling system. In someembodiments, two moderator pistons 1404A, 1404B may be utilized to movemoderator material 1418 back and forth allowing the moderator material1418 to uniformly occupy a constant volume and the neutron detector 1414of the spectrometer 1400 to remain uniformly filled. The moderatorpistons 1404A, 1404B may be configured to remain upright indefinitely.For example, at least one moderator piston 1404A, 1404B may be thickenough to prevent from being physically unseated. The moderator pistons1404A, 1404B may be hollowed out in order to reduce their influence onthe neutron flux through the neutron detector 1414, while maintaininghigh strength. Accordingly, minimal neutron attenuation by thenon-detection and moderation components may be achieved. Alternativemeans of changing the amount of moderator material 1418 present in theneutron moderation section 1416 may include, but are not limited to, aninflatable diaphragm 1420 (see FIGS. 14E and 14F), a viscous boundarylayer separation of moderation fluids, magnetic confinement of magneticmoderator materials, or pressurization (and therefore increased density)of gasses.

The excess moderator reservoir 1406 may be stored behind the neutrondetector 1414 in order to limit back scattering of neutrons into thedetector 1414 or back into the neutron moderation section 1416 causingfalse counts. The excess moderator reservoir 1406 may be configured forsafely storing moderator material 1418 while not in use by thespectrometer 1400. In one embodiment, the excess moderator reservoir1406 may be part of the overall system in order to facilitate mobilityof the spectrometer 1400. For simplicity, the excess moderator reservoir1406 may mirror the neutron moderation section 1416.

The primary component shell 1408 may serve as the housing for any drivecomponents used to move the moderator pistons 1404A, 1404B and may alsocontain the entire neutron detector 1414, including the rear shielding1410, 1412. The rear shielding 1410, 1412 may include two separatecomponents, each designed to reduce the number of false counts talliedby the neutron detector 1414. A thermalizing plate 1410 may beconfigured to reduce thermalized neutrons and capture higher-energyneutrons that attempt to enter the neutron detector 1414 through therear, either through back scattering from stored moderator material 1418or from another neutron source. The thermalizing plate 1410 may include,but is not limited to, borated polyethylene, iron, or steel. A thermalneutron absorbing sleeve 1412 may be configured to act as an alternativeor additional defense against thermalized neutrons entering the neutrondetector 1414 from any direction other than from the front of theneutron detector 1414, thus reducing false counts. The sleeve 1412 mayinclude, but is not limited to, cadmium or borated polyethylene, or anysimilar thermal neutron absorber.

The neutron detector 1414 may be configured to detect thermalizedneutrons and may consist of any number of detectors including, but notlimited to, thin-film coated semiconductor neutron detectors,microstructured semiconductor neutron detectors, gas-filled neutrondetectors, coated wall neutron detectors, coated fin neutron detectors,and the like. In one embodiment, the neutron detector 1414 includes amicrostructured semiconductor neutron detector, such as those producedby the Semiconductor Materials and Radiological Technologies(S.M.A.R.T.) Laboratory at Kansas State University. The selected neutrondetector 1414 may have advantageous qualities such as, but not limitedto, low power requirement for operation, ruggedness, and modular design.The selected neutron detector 1414 may further include high neutrondetection efficiency allowing for good counting statistics fromrelatively short investigation times.

The neutron moderation section 1414 houses the moderator material 1418used for thermalization of neutrons incident on the end of the tube. Theamount of moderator material within the tube can be varied by themoderator pistons 1404A, 1404B, which in turn varies the thickness ofmoderator material 1418 present in front of the neutron detector 1414and thus the path length that an incident neutron is required to travelto the neutron detector 1414 is increased. This allows for variedneutron thermalization within the neutron detector 1414 in a precise andcontrolled manner. Accordingly, knowledge of the amount of neutronmoderator material 1418 present in front of the neutron detector 1414,the type of moderator material 1418, and the number of counts recordedmay be utilized to form a histogram detailing the spectrum of neutronenergies emitted by the source.

The neutron moderator material 1418 may include, but is not limited to,fluid, such as gas or liquid, or a granular or powder material capableof flowing in a continuously variable manner. A continuously variabledesign may allow for an infinite number of discreet measurements,limited only by the system driving the moderator material 1418. In someembodiments, the neutron moderator material 1418 may have a high neutronscatter cross-section and a low neutron absorption cross-section toallow for thermalization, but not absorption, of all energies ofneutrons. In some embodiments, the neutron moderator material 1418 mayinclude water or hydrocarbons.

Neutrons of interest may enter the neutron moderation section 1416 fromthe front of the detector. Therefore the amount of moderator material1418 that the neutrons must past through can be controlled andcalibrated as previously discussed. Neutrons incident from any portionof the spectrometer 1400 other than the aperture may be shielded. Asneutrons enter into the aperture they may pass through any void in theneutron moderation section 1416 until they reach the neutron moderatormaterial 1418. Depending on the energy of the neutrons, they may beginto scatter with a higher probability of scattering forward thanbackwards. This allows for the thermalization of higher energy neutronsfor detection by the neutron detector 1414. Higher energy neutrons mayscatter through more neutron moderator material 1418 than lower energyneutrons. Neutrons with high enough energy may travel through theneutron moderator material and into the neutron detector 1414 where, ifthey have been fully thermalized, they will be tallied. Lower energyneutrons may be attenuated by the same or a similar amount of neutronmoderator material 1418, thus not contributing to the tally.

In an example of an investigation, neutrons from each of the fourprimary energy bins are represented; thermal neutrons (0 to 0.1 eV),epithermal neutrons (0.1 eV to 100 eV), intermediate neutrons (100 eV to1 MeV), and fast neutrons (+1 MeV). When the neutron moderation section1416 is completely filled with neutron moderator material 1418, thevarious neutrons enter into the aperture of the spectrometer 1400, whereonly the high-energy neutrons may be capable of making it through themoderator material 1418 and into the detector 1414. When the neutronmoderation section 1416 is partially filled, as neutron moderatormaterial 1418 is reduced, lower energy neutrons may become able totravel through the moderator material 1418 and into the neutron detector1414. When a minimal amount of neutron moderator material 1418 ispresent, thermal neutrons may be tallied by the neutron detector device1414. As previously discussed, the neutron detector 1414 may beprotected by the rear shielding 1410, 1412 from backscattering neutronsof various energies.

FIGS. 14E and 14F illustrate another embodiment of the variablemoderator thickness neutron spectrometer 1400 that includes an inflatingdiaphragm 1420. The inflatable diaphragm may be configured to controlthe amount of neutron moderator material 1418 between the aperture andneutron detector 1414, allowing a neutron spectrum to be investigated asillustrated in the foregoing example. However, instead of a moderatorpiston 1404A, 1404B controlling the moderator material 1418 present inthe neutron moderation section 1416, a selected amount of the neutronmoderator material 1418 simply fills the flexible diaphragm 1420.

In the present disclosure, the methods disclosed may be implemented assets of instructions or software readable by a device embodied in atangible media, such as memory. Further, it is understood that thespecific order or hierarchy of steps in the methods disclosed areexamples of exemplary approaches. Based upon design preferences, it isunderstood that the specific order or hierarchy of steps in the methodcan be rearranged while remaining within the disclosed subject matter.The accompanying method claims present elements of the various steps ina sample order, and are not necessarily meant to be limited to thespecific order or hierarchy presented.

Those having skill in the art will recognize that the state-of-the-arthas progressed to the point where there is little distinction leftbetween hardware and software implementations of aspects of systems; theuse of hardware or software is generally (but not always, in that incertain contexts the choice between hardware and software can becomesignificant) a design choice representing cost vs. efficiency tradeoffs.Those having skill in the art will appreciate that there are variousvehicles by which processes and/or systems and/or other technologiesdescribed herein can be effected (e.g., hardware, software, and/orfirmware), and that the preferred vehicle will vary with the context inwhich the processes and/or systems and/or other technologies aredeployed. For example, if an implementer determines that speed andaccuracy are paramount, the implementer may opt for a mainly hardwareand/or firmware vehicle; alternatively, if flexibility is paramount, theimplementer may opt for a mainly software implementation; or, yet againalternatively, the implementer may opt for some combination of hardware,software, and/or firmware. Hence, there are several possible vehicles bywhich the processes and/or devices and/or other technologies describedherein may be effected, none of which is inherently superior to theother in that any vehicle to be utilized is a choice dependent upon thecontext in which the vehicle will be deployed and the specific concerns(e.g., speed, flexibility, or predictability) of the implementer, any ofwhich may vary. Those skilled in the art will recognize that opticalaspects of implementations will typically employ optically-orientedhardware, software, and or firmware.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of block diagrams, flowcharts,and/or examples. Insofar as such block diagrams, flowcharts, and/orexamples contain one or more functions and/or operations, it will beunderstood by those within the art that each function and/or operationwithin such block diagrams, flowcharts, or examples can be implemented,individually and/or collectively, by a wide range of hardware, software,firmware, or virtually any combination thereof. In one embodiment,several portions of the subject matter described herein may beimplemented via Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs), digital signal processors (DSPs), orother integrated formats. However, those skilled in the art willrecognize that some aspects of the embodiments disclosed herein, inwhole or in part, can be equivalently implemented in integratedcircuits, as one or more computer programs running on one or morecomputers (e.g., as one or more programs running on one or more computersystems), as one or more programs running on one or more processors(e.g., as one or more programs running on one or more microprocessors),as firmware, or as virtually any combination thereof, and that designingthe circuitry and/or writing the code for the software and or firmwarewould be well within the skill of one of skill in the art in light ofthis disclosure. In addition, those skilled in the art wilt appreciatethat the mechanisms of the subject matter described herein are capableof being distributed as a program product in a variety of forms, andthat an illustrative embodiment of the subject matter described hereinapplies regardless of the particular type of signal bearing medium usedto actually carry out the distribution. Examples of a signal bearingmedium include, but are not limited to, the following: a recordable typemedium such as a floppy disk, a hard disk drive, a Compact Disc (CD), aDigital Video Disk (DVD), a digital tape, a computer memory, etc.; and atransmission type medium such as a digital and/or an analogcommunication medium (e.g., a fiber optic cable, a waveguide, a wiredcommunications link, a wireless communication link, etc.).

In a general sense, those skilled in the art will recognize that thevarious aspects described herein which can be implemented, individuallyand/or collectively, by a wide range of hardware, software, firmware, orany combination thereof can be viewed as being composed of various typesof “electrical circuitry.” Consequently, as used herein “electricalcircuitry” includes, but is not limited to, electrical circuitry havingat least one discrete electrical circuit, electrical circuitry having atleast one integrated circuit, electrical circuitry having at least oneapplication specific integrated circuit, electrical circuitry forming ageneral purpose computing device configured by a computer program (e.g.,a general purpose computer configured by a computer program which atleast partially carries out processes and/or devices described herein,or a microprocessor configured by a computer program which at leastpartially carries out processes and/or devices described herein),electrical circuitry forming a memory device (e.g., forms of randomaccess memory), and/or electrical circuitry forming a communicationsdevice (e.g., a modem, communications switch, or optical-electricalequipment). Those having skill in the art will recognize that thesubject matter described herein may be implemented in an analog ordigital fashion or some combination thereof.

Those skilled in the art will recognize that it is common within the artto describe devices and/or processes in the fashion set forth herein,and thereafter use engineering practices to integrate such describeddevices and/or processes into data processing systems. That is, at leasta portion of the devices and/or processes described herein can beintegrated into a data processing system via a reasonable amount ofexperimentation. Those having skill in the art will recognize that atypical data processing system generally includes one or more of asystem unit housing, a video display device, a memory such as volatileand non-volatile memory, processors such as microprocessors and digitalsignal processors, computational entities such as operating systems,drivers, graphical user interfaces, and applications programs, one ormore interaction devices, such as a touch pad or screen, and/or controlsystems including feedback loops and control motors (e.g., feedback forsensing position and/or velocity; control motors for moving and/oradjusting components and/or quantities). A typical data processingsystem may be implemented utilizing any suitable commercially availablecomponents, such as those typically found in datacomputing/communication and/or network computing/communication systems.

The herein described subject matter sometimes illustrates differentcomponents contained within, or connected with, different othercomponents. It is to be understood that such depicted architectures aremerely exemplary, and that in fact many other architectures can beimplemented which achieve the same functionality. In a conceptual sense,any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected”, or“operably coupled”, to each other to achieve the desired functionality,and any two components capable of being so associated can also be viewedas being “operably couplable”, to each other to achieve the desiredfunctionality. Specific examples of operably couplable include but arenot limited to physically mateable and/or physically interactingcomponents and/or wirelessly interactable and/or wirelessly interactingcomponents and/or logically interacting and/or logically interactablecomponents.

While particular aspects of the present subject matter described hereinhave been shown and described, it will be apparent to those skilled inthe art that, based upon the teachings herein, changes and modificationsmay be made without departing from the subject matter described hereinand its broader aspects and, therefore, the appended claims are toencompass within their scope all such changes and modifications as arewithin the true spirit and scope of the subject matter described herein.

Furthermore, it is to be understood that the invention is defined by theappended claims. It will be understood by those within the art that, ingeneral, terms used herein, and especially in the appended claims (e.g.,bodies of the appended claims) are generally intended as “open” terms(e.g., the term “including” should be interpreted as “including but notlimited to,” the term “having” should be interpreted as “having atleast,” the term “includes” should be interpreted as “includes but isnot limited to,” etc.). It will be further understood by those withinthe art that if a specific number of an introduced claim recitation isintended, such an intent will be explicitly recited in the claim, and inthe absence of such recitation no such intent is present. For example,as an aid to understanding, the following appended claims may containusage of the introductory phrases “at least one” and “one or more” tointroduce claim recitations. However, the use of such phrases should notbe construed to imply that the introduction of a claim recitation by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim recitation to inventions containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations. In addition, evenif a specific number of an introduced claim recitation is explicitlyrecited, those skilled in the art will recognize that such recitationshould typically be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations). Furthermore, in those instances where a conventionanalogous to “at least one of A, B, and C, etc.” is used, in generalsuch a construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, and C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). In those instances where aconvention analogous to “at least one of A, B, or C, etc.” is used, ingeneral such a construction is intended in the sense one having skill inthe art would understand the convention (e.g., “a system having at leastone of A, B, or C” would include but not be limited to systems that haveA alone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). It will be furtherunderstood by those within the art that virtually any disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms. For example, the phrase “A or B” will be understood toinclude the possibilities of “A” or “B” or “A and B.”

Although particular embodiments of this invention have been illustrated,it is apparent that various modifications and embodiments of theinvention may be made by those skilled in the art without departing fromthe scope and spirit of the foregoing disclosure. Accordingly, the scopeof the invention should be limited only by the claims appended hereto.

It is believed that the present disclosure and many of its attendantadvantages will be understood by the foregoing description, and it willbe apparent that various changes may be made in the form, constructionand arrangement of the components without departing from the disclosedsubject matter or without sacrificing all of its material advantages.The form described is merely explanatory, and it is the intention of thefollowing claims to encompass and include such changes.

What is claimed:
 1. An apparatus for determination of one or more freeneutron characteristics, comprising: one or more neutron detectors, theone or more neutron detectors comprising: a plurality of neutrondetection devices; a plurality of discrete neutron moderating elements,wherein each of the neutron moderating elements is disposed between twoor more neutron detection devices, the plurality of neutron detectiondevices and the plurality of discrete neutron moderating elementsdisposed along a common axis; and a control system communicativelycoupled to each of the neutron detection devices, the control systemconfigured to: generating a detector response library, wherein thedetector response library includes one or more sets of data indicativeof a response of the one or more neutron detectors to a known neutronsource; receive one or more measured neutron response signals from eachof the neutron devices, the one or more measured response signalsresponsive to a detected neutron event; and determine one or morecharacteristics of neutrons emanating from a measured neutron source bycomparing the one or more measured neutron response signals to thedetector response library.
 2. The apparatus of claim 1, wherein at leastsome of the neutron detection devices comprise: a micro-structuredsemiconductor neutron detection device.
 3. The apparatus of claim 1,wherein at least some of the neutron detection devices comprise: acoated semiconductor neutron detection device.
 4. The apparatus of claim1, wherein the neutron event comprises: a neutron capture event, aneutron-induced fission event, or a neutron scattering event.
 5. Theapparatus of claim 1, wherein the one or more neutron detectors has acylindrical shape, a spherical shape, a conical shape, a parallelepipedshape, an ellipsoidal shape, or a hexagonal shape.
 6. The apparatus ofclaim 1, wherein at least some of the discrete moderating elements haveat least one of a cylindrical shape and a parallelepiped shape.
 7. Theapparatus of claim 1, wherein at least a portion of the surface of theone or more neutron detectors is covered with an electromagnetic shieldmaterial.
 8. The apparatus of claim 1, wherein at least a portion of thesurface of the one or more neutron detectors is covered with at leastone of a neutron shield and a radiation shield.
 9. The apparatus ofclaim 1, wherein at least some of the neutron detection devices includetwo or more neutron detection elements.
 10. The apparatus of claim 9,wherein the two or more neutron detection elements are distributedaccording to a geometric pattern.
 11. The apparatus of claim 1, whereinat least some of the neutron detection devices are substantially planar.12. The apparatus of claim 1, wherein at least some of the neutrondetection elements are linearly positioned along an orientation axis.13. The apparatus of claim 1, wherein at least some of the neutrondetection elements are nonlinearly positioned along an orientation axis.14. The apparatus of claim 1, wherein the determined one or morecharacteristics of neutrons emanating from a measured neutron sourcecomprise: at least one of energy, energy spectrum, type of neutronsource, direction of neutron emanation, neutron flux, neutron fluence,and neutron dose.
 15. An apparatus for determination of one or more freeneutron characteristics, comprising: one or more neutron detectors, theone or more neutron detectors comprising: a plurality of neutrondetection devices; a plurality of discrete neutron moderating elements,wherein each of the neutron moderating elements is disposed between twoor more neutron detection devices, the plurality of neutron detectiondevices and the plurality of discrete neutron moderating elementsdisposed along a common axis; one or more backscatter blockers disposedin proximity to one or more of the neutron detection devices, the one ormore backscatter stoppers configured to inhibit neutron intensitysmearing along one or more coordinate axes; and a control systemcommunicatively coupled to each of the neutron detection devices, thecontrol system configured to: generate a detector response library,wherein the detector response library includes one or more sets of dataindicative of a response of the one or more neutron detectors to a knownneutron source; receive one or more measured neutron response signalsfrom each of the neutron devices, the one or more measured responsesignals responsive to a detected neutron event; and determine one ormore characteristics of neutrons emanating from a measured neutronsource by comparing the one or more measured neutron response signals tothe detector response library.
 16. The apparatus of claim 15, wherein atleast some of the neutron detection devices comprise: a micro-structuredsemiconductor neutron detection device.
 17. The apparatus of claim 15,wherein at least some of the neutron detection devices comprise: acoated semiconductor neutron detection device.
 18. The apparatus ofclaim 15, wherein the one or more neutron detectors has a cylindricalshape, a spherical shape, a conical shape, a parallelepiped shape, anellipsoidal shape, or a hexagonal shape.
 19. The apparatus of claim 15,wherein at least some of the discrete moderating elements have at leastone of a cylindrical shape and a parallelepiped shape.
 20. The apparatusof claim 15, wherein at least a portion of the surface of the one ormore neutron detectors is covered with an electromagnetic shieldmaterial.
 21. The apparatus of claim 15, wherein at least some of theneutron detection devices include two or more neutron detectionelements.
 22. The apparatus of claim 21, wherein the two or more neutrondetection elements are distributed according to a geometric pattern. 23.The apparatus of claim 15, wherein at least some of the neutrondetection devices are substantially planar.
 24. The apparatus of claim15, wherein the determined one or more characteristics of neutronsemanating from a measured neutron source comprise: at least one ofenergy, energy spectrum, type of neutron source, direction of neutronemanation, neutron flux, neutron fluence, and neutron dose.